He can't. Currently, there is no definitive test or procedure to measure the amount of cannabis in a person's bloodstream if they've been pulled over by a police officer. This is one of the obstacles for the legalization of recreational marijuana.

A reporter from the Hartford Courant, Rebecca Lurye recently spoke with psychology professor and PH.D Michael Milburn during a Capitol Watch podcast. Milburn has recently developed an app called DRUID which stands for DRiving Under the Influence. Click on courant.com to listen to the entire 22-minute podcast.

It should be noted that the Druid app was developed so individuals can find out if they might be too stoned to drive. The app gives you a score from 1 to 100. The higher the number, the greater the impairment. A score greater than 50 means you're in the danger zone and suggests that driving a vehicle is a bad idea. Check out the following video to see how the app works.

The results from the DRUID app can't be used in court in connection with drugged driving because it doesn't determine how much cannabis is actually in the driver's bloodstream although it can be used to help individuals make informed judgments about their current cognitive and physical states.